Engineers are working to develop a system that interworks between a mobile phone capable of communicating in a wide area and a wireless LAN service which enables fast data communication in a relatively small area to cause them to complement each other. Architectures of interworking systems that implement scenarios for accessing packet services of a mobile communication network through a WLAN are standardized in the 3GPP (3rd Generation Partnership Project). Requirements concerning access to packet service of a mobile communication network over a WLAN are described in TS 22.234 Ver. 6.2.0 “Requirements on 3GPP system to Wireless Local Area Network (WLAN) interworking”, Chapter 5, Sep. 27, 2004, http://www.3gpp.org/ftp/Specs/html-info/22234.htm. The architecture is described in TS 23.234 Ver. 6.3.0 “3GPP system to Wireless Local Area Network (WLAN) interworking”, Chapter 6, Jan. 7, 2005, http://www.3gpp.org/ftp/Specs/html-info/23234.htm. The authentication method is described in TS 33.234 Ver. 6.3.0 “Wireless Local Area Network (WLAN) interworking security”, Chapter 6, Dec. 23, 2004, http://www.3gpp.org/ftp/Specs/html-info/33234.htm.
FIG. 9 is a diagram showing a configuration of an interworking system built with a conventional technology. A terminal 901 is capable of making packet access to both of a mobile communication network and a WLAN.
The terminal 901 corresponds to UE (User Equipment) in the 3GPP specifications. A WLAN access network 902 is a packet network using a protocol such as IP (Internet Protocol) and converts a radio signal in a WLAN into a packet signal in a wired network. The WLAN access network corresponds to WLAN AN (Access Network) in the 3GPP specifications. A DHCP server (not shown) in the WLAN access network 902 performs address assignment operation.
A WLAN gateway 903 is connected to the WLAN access network 902 and communicates WLAN control data and user data to and from the WLAN access network 902. The WLAN gateway 903 corresponds to WAG (Wireless Access Gateway) in the 3GPP specifications. A packet data gateway 904 is connected to the WLAN gateway 903 and relays packet data to a public packet-switched network 912. The packet data gateway 904 relays packet data from the public packet-switched network 912 to the WLAN and relays packet data from the WLAN to the public packet-switched network 912. The packet data gateway 904 corresponds to PDG (Packet Data Gateway) in the 3GPP specifications.
A base station 905 in a mobile communication network converts a radio signal from the terminal 901 into a wired signal and transmits the converted signal. The base station 905 corresponds to Node B in the 3GPP specifications. A radio network controller 906 is connected with the base station 905 and performs radio terminal control and transmits control data and user data on the mobile communication network. The radio network controller 906 corresponds to RNC (Radio Network Controller) in the 3GPP specifications. A packet controller 907 is connected to the radio network controller 906, controls packet transmission within the mobile communication network and manages the status of terminals 901 that relates to packet transmission. The packet controller 907 corresponds to SGSN (Serving GPRS Support Node) in the 3GPP specifications. A mobile network packet gateway 908 is connected to the packet controller 907 and relays packet data from the mobile communication network to the public packet-switched network 912 (the Internet). The mobile network packet gateway 908 corresponds to GGSN (Gateway GPRS Support Node) in the 3GPP specifications.
A service server 914 is a server that manages services provided by the mobile communication network. When the services are accessed from the WLAN, the service server 914 is accessed through the packet data gateway 904. A 3G authentication apparatus 909 is connected to the WLAN access network 902 and the packet data gateway 904 and transfers authentication data provided from the terminal 901 and authentication information for the terminal 901. The 3G authentication apparatus 909 corresponds to AAA Server in the 3GPP specifications. A user information storing device 910 stores information about a service provided to a user under an agreement between the user and the carrier of the mobile communication network or the WLAN. The user information storing device 910 is connected with the packet controller 907, the mobile network packet gateway 908, and the 3G authentication apparatus 909.
When a user moves from an area covered by the mobile communication network to the WLAN in the system while making packet access using the terminal 901 capable of accessing both of the mobile communication network and WLAN, mobility transparency to its correspondent node 913 must be ensured in order to maintain communication. To that end, the system has a home address management device 911. The correspondent node 913 is a terminal with which the terminal 901 is performing packet communication. Examples of the correspondent node 913 include a server provided on the Internet. The home address management device 911 relays data transmission from the correspondent node 913 and changes the transfer destination of data in accordance with the location to which the terminal 901 is moving. The position of the terminal 901 is managed and registered using Mobile IP.
The following is a description of a method for the terminal 901 to switch to packet communication over the WLAN when the terminal 901 enters an area of the WLAN while performing packet communication with the correspondent node 913 over the mobile communication network in the system described above.
FIG. 10 shows operation for switching from the mobile communication network to the WLAN. The terminal 901 is performing IP packet communication with the correspondent node 913 through nodes of the mobile communication network and the home address management device 911 (S80). The IP address of the terminal 901 used within the mobile communication network is assigned by the mobile network packet gateway 908. The IP address is referred to as the remote IP address. The home address management device 911 manages the set of the home IP address which is the address of the terminal 901 in the home network and the remote IP address of the terminal 901. The home address management device 911 encapsulates IP packets directed from the correspondent node 913 to the home IP address of the terminal 901 and transmits the encapsulated IP packets. Similarly, the home address management device 911 encapsulates IP packets output from the terminal 901 and then transmits them to the correspondent node 913.
In the mobile communication network, an IP tunnel is created between nodes and IP packets are encapsulated before transmission. GTP (GPRS Tunneling Protocol) is used between the mobile network packet gateway 908 and the packet controller 907 and between the packet controller 907 and the radio network controller 906. In the radio network controller 906, IP packets are converted into a logical channel or transport channel as appropriate and then transferred to the base station 905 using IP transport. The base station 905 converts packets into a physical channel of W-CDMA to communicate with the terminal 901.
When the terminal 901 enters a WLAN area (S82), the terminal 901 detects the radio field of the WLAN and authentication processing for the terminal 901 to use an access point is performed in the WLAN access network 902 (S84). Then, processing for authenticating the user is performed between the WLAN access network 902 and the 3G authentication apparatus 909 (S86). In this processing, the 3G authentication apparatus 909 accesses the user information storing device 910 to authenticate whether the user is a subscriber of an interworking service. After completion of the authentication, the DHCP server in the WLAN access network 902 assigns an IP address to be used for IP communication to the terminal 901 (S88). The IP address assigned here is referred to as the local IP address.
Then, the terminal 901 sends a PDG address resolution request to the packet data gateway 904 (S90). The packet data gateway 904 is a gateway for a terminal to perform IP packet communication with the correspondent node 913 over the WLAN from the mobile communication network. The packet gateway 904 assigns to the terminal 901 an IP address for the terminal 901 to use the WLAN from the mobile communication network.
The terminal 901 sends a tunnel creation request to the packet data gateway 904 for communication over the WLAN (S92). In response to the tunnel creation request, the packet data gateway 904 communicates with the 3G authentication apparatus 909 to perform an authentication completion determining process to determine whether the terminal 901 has been authenticated as a subscriber of the interworking service (S94). Then, authentication setting is performed between the packet data gateway 904 and the WLAN gateway 903 to set information concerning the authenticated terminal 901 in the WLAN gateway 903 (S96). The authentication setting enables control such that packet data received from an unauthenticated terminal is prevented from being transmitted to the data packet gateway 904.
After the authentication setting, tunnel attributes are exchanged between the terminal 901 and the packet data gateway 904 to create a tunnel between them (S98). After the tunnel is created, the terminal 901 registers its remote IP address in the home address management device 911 through the packet data gateway 904 (S100). After the remote IP address is registered, the remote address management device 911 changes the destination of packet transmitted from the correspondent node 913 to the terminal 901 associated with the new remote IP address.
After connection to the WLAN is established in this way (S102), the terminal 901 disconnects communication over the mobile communication network that was used before the terminal 901 enters the WLAN area. This processing is initiated by issuing a 3G disconnection to the packet controller 907 (S104).